NEW TANK PROJECT
CONTENTS 1. INTRODUCTION 2. SELECTION OF SITE 3. OBJECT OF THE PROJECT 4. CAPACITY OF CONTOURS 5. BLOCK LEVEL AT WASTE WEIR 6. BLOCK LEVEL AT SLUICE POINT 7. OFFICE WORK 8. CONCLUSION 9. DRAWINGS
INTRODUCTION Irrigation may be defined as the process of artificially supplying water to soil for raising crops. Irrigation Engineering is an interesting subject to anyone being a student and/or Engineer in service. The purpose of irrigation project is to supply the required amount of water and produce most economically crop yield. For this purpose irrigation project is broadly classified as: 1) Major Irrigation Project. 2) Minor Irrigation Project. 1) MAJOR IRRIGATION PROJECT: It envisages the construction of major works like storage reservoir erected by high dams, a solid diversion weirs, costly head works, ac ross perennial streams. The cost of these projects are generally in crores of rupees. Such projects are always multipurpose to irrigate greater areas. 2) MINOR PROJECTS: These are built generally for any one purpose such as irrigation for small areas, water supply to nearby villages etc., It investigates the construction of low earth bunds across non-perennial streams, low diversion wells etc., The cost of these projects are generally less.
SELECTION OF SITE:
It is very difficult to select a site for a major project i.e., tank satisfying the necessary requirements usually sites satisfying most of t he conditions are selected. Major tanks are usually multipurpose projects and are constructed across the perennial rivers. The sites must be so selected that the river at a dam alignment, runs a straight and does not change course. As far as possible, non-alluvial sites are preferred. Geographically the foundations bed should be capable to serve larger area. The catchment area covers greater region. The site selected at Bandi Halla located 2 kms. Away from S.S. Ghati is not ideal site but can be accepted as good one as all the points regarding the selection of sites are not truly satisfied. But it may be recalled that a site which satisfies all then conditions required does not exists any where, hence Bandi Halla site is a good site. SURVEY TO BE CARRIED OUT FOR NEW TANK PROJECT : 1) L/S and C/S along the centre line of B und.
2) Location of waste water weir and sluice on the centre line of the dam. Carrying block levels at the waste weir and sluice point. 3) Tracing the capacity contours for the following : a) MXL (Max. water level= FTL + Free Board). b) FTL (Full Tank Level). c)
LWL (Low Water Level).
d) Contour corresponding to the sill of the sluice. (The volume of water stored below this gives the dead wate).
LONGITUDINAL AND CROSS SECTION :
A) OBJECT: To estimate the cost of the bund and sluice, the centre line of the bund should be fixed keeping the following points in view. 1) The length of the proposed bund should be minimum. 2) There should be good foundation soil. 3) The natural subsidiary valley is desirable on the bund site for locating the water supply weir.
EQUIPMENT REQUIRED : 1) Theodolite with stand. 2) Level with stand. 3) Levelling staff. 4) Chain with arrows. 5) Tape 6) Wooden pegs. 7) Ranging rods. 8) Compass with stand etc. , PROCEDURE : 1) To establish the bench mark (permanent). 2) Carry fly levels to the dam site and establish the top bund level on either side on the centre of the bund.
3) Carry out the centre line alignment by direct ranging between the two banks, and the drive pegs at suitable (preferably equal) intervals. Establish both the banks with respect to permanent objects, talking bearing and also note down the bearings of the dam centre line with respect to North. 4) Along the so established centre line carry out longitudinal section at every 15 mts. and cross section also every 30 metres. This must be carried out at 5 metres interval both on upstream and downstream side so t hat the edges of the dam is covered on either sides. ( NOTE : At the deepest point you will have to cover larger c hainages while less chainages at higher levels). 5)
Note down the distances to both the ends of the waste weir ( Length say 45 meters) from any one of the banks, similarly to the centre of the sluice. (RL of sluice is given in field).
6) Carryout capacity contour work. Starting from anyone of the bank for MWL, FTL, LWL and sill of sluice, this can be done using level, chain compass or plane table, Locate the contour points at every 15 metres. 7) CAPACITY CONTOURS : a) OBJECT : To fix the storage levels of a reservoir or a tank. b) EQUIPMENT REQUIRED : 1) Level with stand. 2) Levelling staff. 3) Plane table with stand. 4) Alidade. 5) Chain with arrow. 6) Metallic tape. 7) Trough compass. 8) Steel pegs. 9) Ranging rods. c)
PROCEDURE :
1) Starting from the established bench mark levels of the required contours are selected and those points are marked on the plane table drawing sheet. Otherwise by using compass the bearings are taken. 2) Type all lands such as cultivated, barrne, rocky, etc. , are marked on drawing sheets as well as noted in the field work.
BLOCK LEVELS AT WASTE WEIR AND SLUICE PONT SITE : The following points are kept in view while selecting the waste weir etc. , a) 1) There should be a natural diversion channel to carry the surplus weir. 2) There should be good soil available at the site of weir. 3) The length and height of the body wall should be minimum. b)
EQUIPMENT REQUIRED : 1) Level with stand. 2) Levelling staff. 3) Chain with arrows. 4) Tape. 5) Wooden peg. 6) Ranging rods. 7) Compass with stand.
c) PROCEDURE : Block levels are taken at waste weir site intervals of 5 mts. on either side of the centre line of the proposed weir upto a length of 50 mts. from t he centre line on d/s and 30 mts. on u/s side. PHYSICAL FEATURES CONVERSION THE SELECTION OF THE TYPE OF BAND :
1) Topography. 2) Geology and foundation condition. 3) Materials of construction. 4) Length and height of bund. 5) Provision for future expansion. ADVANTAGES AND DISADVANTAGES OF EARTHEEN BUND : ADVANTAGES : 1) Earthen bund can be constructed with natural materials with a minimum of processing and with primitive equipment, which in terms reduces the cost of construction.
2) Earthen bunds don’t require any special type of foundation. They can be constructed on any available foundation. 3) For the construction of Earthen bunds, no skilled labour is required. 4) Future expansion work is possible in a Earthen bund. It can be raised to more height without much difficulty. 5) Earthen bunds are best suited to resist earthquake shocks without danger. DISADVANTAGES : 1) Earthen bunds cannot be used for greater heights. 2) Earthen bunds are more susceptible to failure, as they are less rigid. 3) Heavy rain causes formation of gullies which ultimately leads to the failure of the structure 4) Frequent maintenance is required. 5) Uncontrolled seepage may lead to the failure of the structure. 6) Pags are liable to be damaged by floods and fail without sufficient warning. 7) It requires heavy material and constant supervision.
